The Thinker's Sign

To the Editor:  —Repeated pressure on and friction of the epidermis results in a characteristic hyperkeratotic plaque known as a callus. Production of these lesions requires chronic intermittent stimulation, such as might be a feature of certain occupations—hence, the well-known lesions on the shoulders of hod-carriers, the hands of mechanics, the lips of trumpeters, and the thumbs of leather buffers. There seems to be less appreciation of the fact that certain chronic disease states might result in the widespread adoption of characteristic postures, satisfying the mechanical requirements for callus formation, and consequently resulting in lesions as specific for the disease state as the lesions named are for the corresponding occupations. An example of just such an occurrence is herein described.Bilateral discrete calluses are frequently observed in the suprapatellar areas of patients suffering from chronic pulmonary disease with advanced respiratory insufficiency. The characteristic posture instinctively assumed by patients attempting to